Radiation resistant lubricating grease



United States Patent 3,288,711 RADIATION RESISTANT LUBRICATING GREASE Edwin C. Knowles and Joseph F. Lyons, Poughkeepsie,

and Norman R. Odell, Wappingers Falls, N.Y., assignors to Texaco, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed May 13, 1963, Ser. No. 280,158 9 Claims. (Cl. 25228) This invention relates to the lubrication of machines which are exposed to nuclear radiation and to improved lubricating compositions for such purpose. More particularly, it relates to lubricating greases thickened by finely-divided solids comprising silica and lead silicate.

Lubricating greases exposed to nuclear radiation undergo chemical and physical changes which result in rapid deterioration of their lubricating properties, involving both viscosity changes in the oil base and a breakdown of the grease structure. Greases thickened with finelydivided solids are particularly subject to the latter type of deterioration, due to the effect of nuclear radiation upon the surface energies of the solid particles.

We have found that lubricating compositions of greaselike consistency which are highly resistant to change-s in consistency upon exposure to nuclear radiation, even in high amounts, are obtained by thickening lubricating oils with finely-divided lead orthosilicate in association with additional silica which is present either as a physical mixture or in the form of a complex of some sort with the lead orthosilicate. A preferred thickening agent comprises about 40 80 percent by weight of lead orthosilicate and about 20-60 percent by weight of silica gel, most suitably about 50-75 percent by weight of lead orthosilicate and 25-50 percent by Weight of silica gel. It is suitablyemployed in the form of particles having a diameter below about 70 microns in their maximum dimension, and preferably in the range from about 1 to about 50 microns. The lubricating grease will ordinarily comprise about 20-60 percent by weight, and most suitably about 35-55 percent by weight, of this material.

The lubricating oils employed are preferably hydrocarbon oils, particularly mineral lubricating oils having Saybolt Universal viscosities in the range from about 75' seconds at 100 F. to about 225 seconds at 210 F., high molecular weight aromatic compounds and hydrocarbon polymers in the lubricating oil viscosity range. The preferred mineral oils are distillate oils having viscosities in the range from about 300 seconds at 100 F. to about 100 seconds 'at 210 R, which may be obtained by blending lighter and heavier oils in the lubricating oil viscosity range and which may be either paraflinic or naphthenic in character. Alkylated naphthenes and biphenyl compounds, including alkylated and halogenated naphthenes and biphenyl compounds are especially suitable oils for this purpose.

Synthetic lubricating oils of various types containing other elements in addition to carbon and hydrogen may also be employed to form lubricating greases in accordance with this invention, although the greases thus obtained are less resistant to radiation and therefore less desirable for use in the presence of high amounts of radiation than greases prepared from the hydrocarbon oils described above. Suitable synthetic oils include particularly oxygen and sulfur containing compounds such as diand poly-esters, diand poly-ethers and the sulfur analogs thereof, having viscositie-s within the lubricating oil viscosity range. Examples of suitable diesters include di-Z-ethylhexyl sebacate, di(secondary amyl) sebacate, di-Z-ethylhexyl azelate, di-iso octyl adipate, etc. Particularly suitable polyesters are those described in US. 2,628,974, obtained by reacting an aliphatic dicarboxylic acid with a glycol and a mono-functional aliphatic alcohol or acid.

The lubricating greases of this invention are readily prepared by mixing together the oleaginous liquid and the siliceous material in suitably finely-divided form as discussed above so as to efiectively disperse the siliceous material in the oleaginous liquid. If desired, the grease may be produced by adding the siliceous material to the oil and milling the slurry thus produced, suitably in a mill of the type employed to grind paint pigments.

The preferred siliceous materials employed in these compositions are coprecipitates of lead orthosilicate and silica gel, which are readily obtained by reacting sodium orthosilicate with lead tetrachloride and hydrochloric acid simultaneously. The reaction is suit-ably carried out at room temperature by merely adding a solution of lead tetrachloride and hydrochloric acid to an equeous solution of sodium orthosilicate, employing the lead tetrachloride -and sodium orthosilicate in suitable proportions to give a precipitate comprising about 40-80 percent by weight of lead orthosilicate and sufficient hydrochloric acid to react with the remainder of the sodium orthosilicate and to provide a pH of about 36 in the solution. The precipitate obtained in this manner is washed with water to remove excess hydrochloric acid and dried. It is reduced to the desired'par-ticle size by any convenient means, such as by milling in a ball mill or jet energy mill and classifying by conventional methods.

Additives of the types ordinarily employed in lubricating greases, such as oxidation inhibitors, corrosion inhibitors, tackiness agents, such as various high polymer materials, extreme pressure agent-s, fillers, etc., may be employed in these greases also, as well as minor amounts of various other thickening agents. As examples of particularly suitable corrosion or rust inhibitors may be mentioned metal salts of wax benzene sulfonates, metal salts of petroleum sulfonates, lauryl phosphate, sorbitol monoole'ate and glycerol monostearate. Suitable oxidation inhibitors include phenyl alphanaphthylamine, diphenyl paraphenylene diamine, tetramethyl diamino'diphenyl methane and bis(2-hydroxy-3-t-butyl-5-methylphenyl)methane.

. With particular advantage, at surface-active agent, for example, a quaternary ammonium salt of a fatty acid, a polyglycol ether, a metal alkyl sulfate or sulfonate, etc., may be employed in the greases of this invention in order to improve their water-resistance and emulsification characteristics. The-surface-active agent may be added at any time during the grease preparation. It is most advantageously employed to treat the lead silicate material before the latter is combined with the oil component.

The following example is given for the purposes of further disclosing the invention.

Example I A grease which is representative of the grease of this invention has the following composition in percent by weight:

Lead silicate material 50 Mineral lubricating oil 50 The lead silicate material is a coprecipitate of lead orthosilicate and silica gel, comprising 63.4 percent by weight of lead orthosilicate and the remainder silica gel, in the form of particles ranging from about 44 microns in diameter down to about 3-5 microns in diameter. It is obtained in the manner described hereinabove by combining 151 grams of sodium orthosilicate in aqueous solution with 73.9 grams of lead tetrachloride in hydrochloric acid solution, washing and drying the precipitate,

3 milling it in a ball mill and sieving through a 325 mesh sieve.

The mineral lubricating oil is a 2l.7 API gravity refined naphthenic distillate oil having a Saybolt Universal viscosity of 313 seconds at 100 F. and 47.5 seconds at 210 F. Y r

The grease preparation is carried out by mixing the lead silicate material with an equal weight of lubricating oil and milling the mixture with two passes through a Premier Colloid mill at 0.002 inch clearance. A smooth N.L.G.I. No. 2 grade grease of good appearance and very superior resistance to changes in consistency and other undesirable effects when subjected to a large amount of radiation, in addition to very satisfactory lubricating properties generally is obtained.

The following table shows the radiation resistance of the above grease in a test wherein it is subjected to a high amount of nuclear radiation. The test comprises statically radiating the test sample (about 2 ounces) in a sealed heavy wall Pyrex glass capsule enclosed in a stainless steel cylinder, employing a cobalt-60 radiation source possessing a high specific activity of 45 cu ries per gram. The sample is subjected to the gamma rad-iation of the cobalt-60 for 50 hours for a total dosage of rads, and a determination made of the changes in both its unworked and Worked penetration. The table also shows representative results obtained upon greases thickened with other thickeners in mineral base oils having substantially the same resistance to radiation change as determined in separate tests.

As shown by the above table, the grease thickened with the coprecipitated lead silicate-silica compound underwent only a small amount of softening on the basis of both unworked and worked penetrations in the radiation test, while all of the other greases softened very substantially, the greases thickened with carbon black and with arylurea becoming semi-fluid upon working as a result of the radiation.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim: Y

1. An improved method for the lubrication of a machine subjected to nuclear radiation which comp-rises supplying to the lubricated parts thereof a lubricant composition consisting essentially of a lubricating oil thickened to a grease consistency by a finely-divided siliceous material consisting essentially of 40 to 80 percent by weight of lead orthosilicate and 20 to 60 percent by weight of silica, said siliceous material being present inthe'composition in an amount of from about 20 to about 60 percent by weight, based on the weight of the composition.

2. The method of claim 1 wherein the said siliceous material is a coprecipitate of lead orthosilicate and silica gel comprising about 50-75 percent by weight of lead orthosilicate.

3. The method of claim 1 wherein the said lubricating oil is a hydrocarbon oil selected from the class consisting of mineral oils and alkylated naphthenes and biphenyl compounds.

4. A lubricant composition of improved stability toward atomic radiation which comprises a lubricating oil thickened to a grease consistency with a finely-divided siliceous material consisting essentially of 40 to percent by weight of lead or-thosilicate and 20 to 60 percent by weight of silica, said siliceous material being present in the composition in an amount of from about 20 to about 60 percent by weight, based on the Weight of the composition.

5. The composition of claim 4 wherein the said siliceous material is a coprecipitate of lead orthosilicate and silica gel comprising about 50-75 percent by weight of lead orthosilicate.

6. The composition of claim 4 wherein the said siliceous material is present in an amount from about 35 to about 55 percent by weight of the composition.

7. The composition of claim 4 wherein the said lubricating oil is an oil selected from the group consisting of an alkylated naphthene, an alkylated biphenyl, an alkylated and halogenated naphthene and an alkylated and halogenated biphenyl.

8. The composition of claim 4 wherein the said lubricating oil is mineral oil having a Saybolt Universal viscosity in the range from about 75 seconds at F. to about 225 seconds at 210 F. v

9. The composition of claim 4 wherein the said lubricating oil is a refined naphthenic distillate oil having a Saybolt Universal viscosity of about 313 seconds at 100 F. and about 47.5 seconds at 210 F.

References Cited by the Examiner UNITED STATES PATENTS 2,742,345 4/ 1956 Kloepfer et a1 25228 2,892,776 6/1959 Lyons et al. 25228 2,948,679 8/1960 Rees et a1. 252.-25 X 2,967,827 1/1961 Bolt et a1. 25228 2,981,685 4/196'1 Loefiler 25228 3,028,334 4/1962 Wilson 25221 X FOREIGN PATENTS 659,407 3/ 1963 Canada.

659,408 3/1963 Canada.

659,410 3/1963 Canada.

659,412 3/1963 Canada.

819,023 8/19'59 Great Britain.

914,772 1/1963 Great Britain.

DANIEL E. WYMAN, Primary Examiner.

I. VAUGHN, Assistant Examiner. 

4. A LIBRICANT COMPOSITION OF IMPROVED STABILITY TOWARD ATOMIC RADIATION WHICH COMPRISES A LUBRCATING OIL THICKNENED TO A GREASE CONSISTINCY WITH A FINELY-DIVIDED SILICEOUS MATERIAL CONSISTING ESSENTIALLY OF 40 TO 80 PERCENT BY WEIGHT OF LEAD ORTHOSILICATE AND 20 TO 60 PERCENT BY WEIGHT OF SILICA, SAID SILICEOUS MATERIAL BEING PRESENT IN THE COMPOSITION IN AN AMOUNT OF FROM BOUT 20 TO ABOUT 60 PERCENT BY WEIGHT, BASED ON THE WEIGHT OF THE COMPOSITION. 